The pharmacological modification of reperfusion injury with particular reference to calcium fluxes in the isolated rat heart

Myocardial reperfusion injury is thought to be caused by reperfusion induced i) cytosolic Ca²⁺ overload and/or, ii) the formation of oxygen derived freeradicals. At the start of this study, data implicating cytosolic Ca²⁺ overload in the genesis of reversible reperfusion injury were inconclusive. Although several workers have approached this problem by measurements of cytosolic calcium ions, it was my aim to examine the potential sources of such calcium overload. The experiments reported in this thesis were therefore designed to examine the role of altered intracellular and transsarcolemmal Ca²⁺ fluxes in the genesis of reperfusion stunning and arrhythmias. The study was also aimed at elucidating the possible sources and entry pathways contributing to this proposed cytosolic Ca²⁺ overload. In order to investigate the possible role of altered reperfusion Ca²⁺ fluxes in reperfusion injury, we exposed the isolated working, and Langendorff perfused rat heart model to ischaemia and reperfusion to induce reperfusion stunning and arrhythmias. Hearts were pre-treated (before ischaemia) or reperfused with pharmacological compounds, or by interventions known to enhance or inhibit intracellular or transsarcolemmal Ca²⁺ fluxes. The severity of reperfusion stunning (mechanical dysfunction) was measured by reperfusion aortic output, coronary flow and left ventricular pressure. The incidence of reperfusion ventricular arrhythmias was measured by the incidence of ventricular tachycardia and/ or fibrillation. In selected studies, the metabolic status of hearts was evaluated using biochemical assays performed on myocardial tissue samples. Data obtained in these studies indicate that increased Ca²⁺ fluxes through sarcolemmal L-type Ca²⁺ channels during early reperfusion exacerbate stunning, while inhibition of these fluxes with the Ca²⁺ antagonist drug nisoldipine or by Mg²⁺ or Mn²⁺ improve reperfusion function. These data also suggest that although interventions increasing Ca²⁺ fluxes early in reperfusion exacerbate reperfusion stunning, these same interventions improve reperfusion function when performed later. The data also indicate that Ca²⁺ may enter the myocyte indirectly via activation of the Na⁺/H⁺ and Na⁺/Ca²⁺ exchanger during reperfusion. Inhibition of Na⁺/H⁺ exchange activity by HOE 694 during reperfusion attenuated reperfusion stunning and arrhythmias. Both activation of the Na⁺/H⁺ (and Na⁺/Ca²⁺) exchanger and Ca²⁺ influx via the Ca²⁺ channel could contribute to reperfusion induced Ca²⁺ overload and subsequent injury. The study also showed that altered intracellular Ca²⁺ oscillations play a role in reperfusion stunning and arrhythmias as shown by the use of the SR Ca²⁺ release channel blocker, ryanodine. Inhibition of the sarcoplasmic reticulum Ca²⁺ A TP-ase pump by two novel inhibitors, thapsigargin and cyclopiazonic acid, during ischaemia and early reperfusion improved reperfusion function and reduced the incidence of ventricular arrhythmias. function when unphysiologically high concentrations of the peptide were infused into the heart during reperfusion. Taken together, these data suggest that: 1) Ca²⁺ fluxes during early reperfusion (intracellular and transsarcolemmal) play a role in reperfusion injury, 2) that both the Ca²⁺ channel and Na⁺/H⁺ exchange activity contribute to reperfusion injury by possibly contributing to cytosolic Ca²⁺ overload and that, 3) altered intracellular Ca²⁺ oscillations through the SR play a role in both stunning and arrhythmias. Thus the proposal is that modulation of Ca²⁺ fluxes through either the sarcolemma or the sarcoplasmic reticulum, lessen reperfusion injury (stunning and arrhythmias). Although these data do not provide direct evidence of reperfusion Ca²⁺ overload, they support the concept that calcium ions play a role in the genesis of reversible reperfusion injury

‘Face-to Face vs. Flipped’: A Comparative Study on Academic Outcomes and Learning Preferences in First Year Allied Health Students Undertaking Anatomy and Physiology

[EN] A mixed-mode or ‘‘flipped’’ model of learning focusses on supporting a high level of student engagement, student motivation, and the transferability of specific course content. A blend of online resources and face-to-face (F2F) learning facilitates meaningful interaction between peers, while building a capacity for self-directed and lifelong learning. Within the School of Medical Science, Anatomy and Physiology (A&P) content was ‘flipped’ for delivery at a new campus to align with the traditional F2F offering. Lectures were delivered online, while tutorials and practicums were F2F.. Collaborative learning opportunities utilizing active learning pedagogies was appealing and was integrated during the re-alignment of A&P which was delivered to a cohort of allied health students undertaking their first year of their program. This study assessed how this type of learning was received by students (from the same program) undertaking the same course in an on-campus F2F delivery. Students completed surveys relating to their experiences in learning activities applied in: lectures, tutorials and practicums. In addition, academic outcomes (theoretical and practical) across the two modalities were also evaluated. Overall, students undertaking the mixed-mode delivery performed significantly better in theoretical assessments, while performance in practical assessments was comparable between both deliveries. Student preferences to learning and teaching activities was mixed, however all students highly valued the use of “mini-quizzes” in lectures, tutorials and practicums.Wendt, L.; Du Toit, E.; Naug, H. (2021). ‘Face-to Face vs. Flipped’: A Comparative Study on Academic Outcomes and Learning Preferences in First Year Allied Health Students Undertaking Anatomy and Physiology. En 7th International Conference on Higher Education Advances (HEAd'21). Editorial Universitat Politècnica de València. 1043-1052. https://doi.org/10.4995/HEAd21.2021.13017OCS1043105

Myocardial Insulin Resistance: An Overview of Its Causes, Effects, and Potential Therapy

Abstract: Insulin resistance ensues when normal physiological concentrations of insulin are unable to induce effective cellular insulin signalling and glucose uptake by insulin sensitive tissues. It is caused by several abnormalities that include; 1) an overabundance of circulating free fatty acids (and dyslipidaemia), 2) systemic inflammation caused by increased tissue and circulating pro-inflammatory cytokines, and, 3) over activation of the systemic and organ specific renin-angiotensin systems. Although usually associated with obesity, insulin resistance is not a condition that only afflicts obese individuals. Dyslipidaemia which is implicated in the aetiology of insulin resistance can be caused by adipose tissue expansion (obesity) or the increased consumption of lipogenic fructose which has profound effects on liver metabolism and serum lipid profiles. The primary reason fructose is implicated in insulin resistance is because it induces hepatic lipogenesis which would directly contribute to dyslipidaemia and increased lipid deposition in adipose tissue, muscle (heart and skeletal) and the liver. These changes in tissue lipid content and utilisation are thought to compromise tissue insulin signalling and induce insulin resistance. Myocardial insulin resistance not only influences myocardial metabolism and mechanical function in the normoxic heart but also compromises myocardial tolerance to ischaemia/reperfusion and post-ischaemic outcomes. Once insulin sensitive organs become insulin resistant, their substrate metabolism is altered and in the case of the heart, cardiac mechanical function is compromised which could potentially contribute to heart failure. Insulin resistance also decreases myocardial tolerance to ischaemia and reperfusion by compromising myocardial metabolism during ischaemic/reperfusion. Recently emerged evidence also suggests that insulin resistance reduces myocardial tolerance to ischaemia and reperfusion by altering the functionality of the intrinsic pro-survival Reperfusion Injury Salvage Kinase (RISK) pathways that protect against ischaemia/reperfusion injury. The authors and others have demonstrated strong links between reduced expression and activation (phosphorylation) of components of the RISK pathway and increased myocardial susceptibility to ischaemia/reperfusion injury. Lifestyle changes are known to improve insulin sensitivity while several pharmacological interventions using metabolic modulators and insulin sensitizer are currently being investigated and have shown promise in the treatment of animals and patients with myocardial insulin resistance. This review will identify and highlight some of the proposed causes of insulin resistance with particular reference to the role of dyslipidaemia, inflammation and the rennin-angiotensin system in the aetiology of this condition. We will also explore the possible effects of high dietary fructose consumption on circulating lipids and inflammation and the implications of these changes on skeletal and cardiac muscle insulin sensitivity. We will briefly reflect on the adverse effects of myocardial insulin resistance on myocardial metabolism and mechanical function and assess the effects of insulin resistance on myocardial tolerance to ischaemia and reperfusion. The proposed cellular causes of this decreased myocardial tolerance to ischaemia will be identified and current lifestyle and pharmacological interventions utilised to alleviate these adverse effects of insulin resistance will be reviewed. Keywords: Insulin resistance, Dyslipidaemia, Lipotoxicity, Adipocytokines, Renin-angiotensin system, Myocardial ischaemia/reperfusion.Griffith Health, School of Medical ScienceFull Tex

Impact of dietary-induced obesity on adrenergic-induced cardiomyocyte damage in rats

Although obesity is an independent risk factor for heart failure and even mild-to-moderate forms of obesity are associated with myocardial systolic dysfunction the mechanisms of the myocardial dysfunction have not been identifi ed. We assessed whether dietary-induced obesity is associated with an increased sensitivity of the myocardium to ß-adrenergic-induced cardiomyocyte apoptosis or fibrosis. To induce obesity, rats were fed a diet that promotes an increased caloric intake. Adrenergic-induced cardiomyocyte apoptosis was determined by injecting rats for 5 days with isoproterenol (0.01 mg/kg/day for 3 days and 0.02 mg/kg/day for 2 days) and then studying the degree of cardiomyocyte damage using a TUNEL assay and assessing the pathological score. Five months of feeding rats a diet that promoted the development of an increased body weight (Control=481±4.3 g, Diet=550±7.8 g, p‹0.001) and visceral fat content (Control=19.6±0.8 g, Diet=33.0±1.2 g, p‹0.0001), did not alter baseline cardiomyocyte apoptosis. However, 5 days of ß-adrenergic activation resulted in an enhanced cardiomyocyte apoptosis in rats receiving the experimental diet as compared to rats receiving a normal diet (p‹0.01). No changes in the myocardial pathological score (fibrosis) were noted. The enhanced adrenergic-induced cardiomyocyte apoptosis in obese rats could not be explained by dietary-induced increases in baseline left ventricular internal diameters, decreases in systolic function (endocardial or midwall fractional shortening) or differences in the response of the heart to adrenergic-induced increases in inotropic or chronotropic function. In conclusion, the present study suggests that obesity may contribute to myocardial dysfunction by increasing the sensitivity of the myocardium to adrenergic-induced cardiomyocyte damage

The effect of dietary red palm oil on the functional recovery of the ischaemic/reperfused isolated rat heart: the involvement of the PI3-Kinase signaling pathway

We have previously shown that dietary red palm oil (RPO) supplementation improves functional recovery in hearts subjected to ischaemia/reperfusion-induced injury. Unfortunately, the cellular and molecular mechanisms responsible for this phenomenon are still poorly understood and no knowledge exists regarding the effects of RPO supplementation on the phosphoinositide 3-kinase (PI3-K) signaling pathway and apoptosis during ischaemia/reperfusion injury. Therefore, the aims of the present study were three fold: (i) to establish the effect of RPO on the functional recovery of the heart after ischaemia/reperfuion injury; (ii) to determine the effect of the PI3-K pathway in RPO-induced protection with the aid of an inhibitor (wortmannin); and (iii) to evaluate apoptosis in our model. Wistar rats were fed a standard rat chow control diet or a control diet plus 7 g RPO/kg for six weeks. Hearts were excised and mounted on a Langendorff perfusion apparatus. Mechanical function was measured after a 25 min period of total global ischaemia followed by 30 minutes of reperfusion. Hearts subjected to the same conditions were freeze-clamped for biochemical analysis at 10 min during reperfusion to determine the involvement of the PI3-Kinase signaling pathway and apoptosis in our model. Dietary RPO supplementation significantly increased % rate pressure product recovery during reperfusion (71.0 ± 6.3% in control vs 92.36 ± 4.489% in RPO; p < 0.05). The % rate pressure product recovery was significantly reduced when wortmannin was added during perfusion (92.36 ± 4.489% in the RPO group vs 75.21 ± 5.26% in RPO + Wm). RPO + Wm also significantly attenuated PI3-K induction compared with the RPO group (59.2 ± 2.8 pixels in RPO vs 37.9 ± 3.4 pixels in RPO + Wm). We have also demonstrated that PI3-K inhibition induced PARP cleavage (marker of apoptosis) in the hearts during ischaemia/reperfusion injury and that RPO supplementation counteracted this effect

AJP-supplementary data

Supplementary dat